Here are six possible candidates:
It was kind of a surprise when the face of the NHL was left off the original roster to begin with, so this would be a good opportunity to bring him back into the all-star fold. The Penguins captain has picked it up of late as well with 10 points in his last seven games.
He's cooled off from a surprisingly hot start, but the Devils' leading scorer would be a suitable replacement sniper. His 38 points in 42 games has him seventh in the Metro.
Having a solid season (eight goals, 28 assists for 36 points), and would compliment Claude Giroux nicely in the 3-on-3 tournament. His overtime winner against the Capitals was a nice snapshot of the damage he could do in Nashville.
Derick Brassard/Mats Zuccarello
These two are both having similarly strong years (17 goals and 19 assists for Brassard, 18 goals and 17 assists for Zuccarello), and this would allow the NHL to send more than just Ryan McDonagh from their largest American market. Either choice would work fine.